1. Field of the Present Invention
The present invention relates generally to electromagnetic tomography, and, in particular but not exclusively, to electromagnetic tomography solutions for use with the heads of humans and other animals.
2. Background
Stroke is the 2nd leading cause of death after ischeamic heart diseases, and is responsible for 4.4 million deaths (9 percent of all deaths) each year. According to American Heart Association/Stroke Association, every 40 seconds someone in America has a stroke. Every 3 minutes, someone dies of one. Stroke kills more than 137,000 Americans a year. About 795,000 Americans each year suffer a new or recurrent stroke. In Europe there are approximately 1.1 million deaths each year; in the EU there are approximately 460,000 deaths each year caused by stroke disease.
Stroke is a leading cause of serious, long-term disabilities worldwide, causing significant economic impact. The Potential Years of Life Lost (PYLL) calculated by OECD shows a significant number, which should be preventable.
Acute ischemic strokes account for about 85% of all strokes; each begins with a blood clot (thrombus) forming in the circulatory system at a site distant from the brain. The clot breaks away from this distant site forming an embolus which then travels through the circulatory system; on reaching the brain, the embolus lodges in the small vessels, interrupting blood flow to a portion of brain tissue. With this reduction in blood flow, tissue damage quickly ensues. Clinical management of stroke has been enhanced by the use of thrombolytics (clot busters) combined with the application of brain imaging techniques that reveal the pathophysiological changes in brain tissue that result from the stroke. In particular, the clinical decision to use a thrombolytic must be made within 3 hours of the onset of symptoms and requires a firm diagnosis of an ischemic stroke. This clinical decision currently relies on imaging methods such as computed tomography (CT) and magnetic resonance imaging (MRI) to reliably determine ischemic perfusion changes. Subsequent management of the stroke is enhanced by imaging the extent of the area of brain tissue with compromised blood flow. Current clinical imaging methods, including CT, positron emission tomography (PET) and MRI each offer useful information on tissue properties related to perfusion, ischemia and infarction.
While each of these methods has its own advantages, none currently offers a rapid or cost effective imaging solution that can be made widely available at the “bedside” in the emergency department or to first response paramedical services. Electromagnetic tomography (EMT), on the other hand, is a relatively recent imaging modality with great potential for biomedical applications, including a non-invasive assessment of functional and pathological conditions of biological tissues. Using EMT, biological tissues are differentiated and, consequentially, can be imaged based on the differences in tissue dielectric properties. The dependence of tissue dielectric properties from its various functional and pathological conditions, such as blood and oxygen contents, ischemia and infarction malignancies has been demonstrated.
Two-dimensional (2D), three-dimensional (3D) and even “four-dimensional” (4D) EMT systems and methods of image reconstruction have been developed over the last decade or more. Feasibility of the technology for various biomedical applications has been demonstrated, for example, for cardiac imaging and extremities imaging.
As in any biomedical imaging, the classical EMT imaging scenario consists of cycles of measurements of complex signals, as scattered by a biologic object under study, obtained from a plurality of transmitters located at various points around the object and measured on a plurality of receivers located at various points around the object. This is illustrated in FIG. 1. As recounted elsewhere herein, the measured matrix of scattered EM signals may then be used in image reconstruction methods in order to reconstruct 3D distribution of dielectric properties of the object, i.e., to construct a 3D image of the object.
Generally, it is very important for image reconstruction to precisely describe a distribution of EM field with an imaging domain 21. The distribution of EM field with an imaging chamber is a very complex phenomenon, even when there is no object of interest inside.
FIG. 2 is a schematic view of a prior art EM field tomographic spectroscopic system 10, and FIG. 3 is a schematic diagram illustrating the operation of the system of FIG. 2 in a two-dimensional context. Such a system 10 could carry out functional imaging of biological tissues and could also be used for a non-invasive mapping of electrical excitation of biological tissues 19 using a sensitive (contrast) material (solution or nanoparticles) injected into the biological tissue 19 or carried in the circulation system, characterized by having dielectric properties that are a function of electrical field, generated by biological excited tissue 19. As illustrated in FIG. 2, the system 10 included a working or imaging chamber 12, a plurality of “EM field source-detector” clusters 26, an equal number of intermediate frequency (“IF”) detector clusters 28, and a control system (not shown). Although only two EM field source-detector clusters 26 and two IF detector clusters 28 are shown, a much larger number of each are actually used.
The imaging chamber 12 is a watertight vessel of sufficient size to accommodate a human body or one or more parts of a human body together with a matching liquid. The imaging chamber 12 and its EM field clusters 26, as well as the IF detector clusters 28, have sometimes been mounted on carts in order to permit the respective components to be moved if necessary, and the carts may then be locked in place to provide stability.
Oversimplified, the system 10 operates as follows. An object of interest (e.g., biological tissue) is placed in the imaging domain 21. The transmitting hardware generates electromagnetic (EM) radiation and directs it to one of the antennas. This antenna transmits electromagnetic waves into imaging domain 21, and all of the other antennas receive electromagnetic waves that have passed through some portion of the imaging domain 21. The receiving hardware detects the resulting signal(s), and then the same cycle is repeated for the next antenna and the next one until all antennas have served as a transmitter. The end result is a matrix of complex data which is transmitted to one or more computers in the control system that process the data to produce an image of the object 19 in the imaging domain 21. An algorithm called an “inversion” algorithm is utilized in this process.
Electromagnetic tomography uses non-ionizing electromagnetic radiation to differentiate between human tissues. Using a compact antenna design, it creates a low power EM field (less than used in cellular phones), which interacts with the biological object and is then measured by sensors. Special imaging algorithms are then used to inverse a “data tensor” and reconstruct a 3D distribution of dielectric properties within a biological subject inside the EM field—i.e. to obtain a so-called “image tensor” or, simply, an image of the object. These imaging algorithms are in very general terms similar to the ones used in classical imaging methods (such as back-projection method used in Computed Tomography (CT)). However, the wave nature of propagation of EM waves needs to be accounted for in imaging algorithms, siginificantly complicating them. In addition, EMT imaging of the brain presents a significant challenge, as the brain is an object of interest that is located inside a high dielectric contrast shield, comprising the skull (with low dielectric contrast (∈˜10-15) and cerebral spinal fluid (with high ∈˜55-60)).
The images are possible due to the contrast in dielectric properties of various tissues. The contrasts in dielectric properties can also be mapped between normal tissues and tissues under different functional or pathological conditions (functional contrasts). Examples include: malignancies in breast, liver and lung; tissue blood content/flow; hypoxia; ischemia; infarction; compartmental injury; stroke; and brain trauma.
Unfortunately, existing EMT solutions are not well-suited for certain applications. In this regard, FIGS. 4 and 5 are schematic illustrations of two three-dimensional settings for the system of FIG. 2. As evident therefrom, conventional EMT imaging chambers are oriented vertically so as to hold the matching liquid. Such an arrangement makes it very difficult to use the technology to image a human head because of the inconvenience of positioning a patient's head in the imaging chamber. This is particularly problematic in the emergency setting, where a patient may not be capable of positioning himself in an arrangement that allows him to insert his head into the imaging chamber. As a result, current implementations of EMT technology are not very suitable for use in diagnosing or treating stroke. Thus, a need exists for a safe, portable and cost-effective supplement to current imaging modalities for acute and chronic assessment of cerebral vascular diseases, including stroke. In particular, a need exists for the use of EMTensor technology in a mobile setting, such as in an ambulance or helicopter, and continual, safe and cost effective monitoring of an efficacy of treatment in ICUs and other medical facilities.